1. Field of the Invention
This invention relates to the field of internal combustion engines and more particularly to carbureted fuel/air induction systems for such engines wherein heat is employed to vaporize liquid fuel inducted into the engine cylinders.
2. Description of the Prior Art
Carburetors for internal combustion engines have been known as long as the engines, per se. Nearly all employ some form of Venturi air passage, one or more throttle valves for restricting the entry of air into the passage, a liquid fuel reservoir, and one or more fuel jets through which liquid fuel is aspirated into the air passage by the flow of air therethrough. The fuel/air mixture from the carburetor is inducted into an intake manifold which distributes the mixture to the respective engine cylinders.
In nearly all present-day carbureted fuel induction systems, the fuel/air mixture delivered to the engine cylinders is comprised of air, vaporized fuel, and unvaporized liquid fuel droplets. This mixture is compressed and burned with a cylinder to generate power. The burning process involves the direct chemical reaction of the carbon and hydrogen content of the liquid fuel with the oxygen content of the air. The reaction is exothermic and the by-products of combustion include: carbon dioxide, water vapor, carbon monoxide, nitrous oxide and unburned hydrocarbons. The latter three are considered undesirable emissions, or air pollutants, and also represent wasted chemical energy. The allowable levels of these emissions is currently regulated closely by law and are the subject of much controversy.
A fundamental premise of the present invention presumes that the majority of the unburned hydrocarbons emitted through the engine exhaust is caused by the incomplete combustion of the fuel delivered to the cylinders in droplet form. This is predicated on the fact that the time for combustion during the power stroke of a piston is very short, and the chemical reaction that takes place requires that molecules of oxygen be in the immediate proximity of fuel molecules within this time span. The fuel molecules with the fuel droplets are effectively encased within a coating of other fuel molecules and an outer coating of molecules that have already reacted with oxygen. The unburned cores of the droplets are discharged through the engine exhaust.
Numerous attempts have been made to vaporize the fuel prior to delivery to the engine cylinders by application of heat to the fuel/air mixtures. Most of these attempts have failed because the application of heat in this manner also heats the incoming air causing it to expand - with a corresponding loss in volumetric efficiency. The power generated within an engine cylinder depends on the weight of the burned fuel/air mixture - not its volume.
In modern-day automotive engines, the fuel/air mixture inducted through the carburetor is caused to impinge against a heated surface within the intake manifold. This surface is generally heated by exhaust gases or by water circulated through the engine cooling jacket. The fuel droplets that impinge against the heated surface evaporate and return to the intake air stream. The great majority of the fuel droplets flow directly with the air stream to the engine cylinders. If the heated surface is too hot, the fuel droplets that impinge boil off violently and return to the air stream in droplet form.
In my prior U.S. Pat. No. 3,821,941 entitled: Valving for Internal Combustion Engine, I described a system for inducting a fuel/air mixture into a 2-cycle engine cylinder as a rapidly swirling mass. A portion of the exhaust gases from the prior cycle was entrapped with the incoming mixture and could cause self-ignition of the mixture due to the combined heat of the exhaust gas and heat of compression produced by the piston. It was also observed in this system that leaner than conventional fuel/air mixtures could be fired, with a measured increase in power output. It was presumed that the thorough intermixture of the rapidly swirling incoming mixture with the hot exhaust gases caused better chemical combination of the fuel and air. The heat due to the entrapped exhaust gases was also effective to break up fuel droplets in the inducted mixture, as evidenced by the lower exhaust emissions.
It is apparent that the fuel inducted into a cylinder should be completely vaporized prior to combustion. In Diesel engines, the liquid fuel is injected as a finely atomized mist. The mist is liquid fuel in droplet form, and the black smoke ejected under some operating conditions, particularly wide-open-throttle, is visual evidence of incomplete combustion.